Patients are crowding hospital emergency rooms, physician offices and urgent-care clinics as the flu season picks up across the Rock River Valley.

Winnebago County Health Department surveillance reports show that 54 cases of influenza were reported for the last week of December, the most recent information available. The department gets the data voluntarily from hospitals, long-term care facilities and schools.

Reports are expected to increase this month.

The 2012-13 flu season hit hard and early. It came on strong in December 2012, but the flu season typically peaks in January or February.

"The flu season has not been as drastic as in years' past, but the third week of January and the last week of February, first week of March are the worst times," said Craig Beintema, Stephenson County Health Department administrator. "There's always a data lag between us and the hospitals, so it can still get worse."

Influenza is being reported in people who received the flu shot and those who didn't, said Kara Biery, director of health protection and promotion at the Winnebago County Health Department.

"For those who have been vaccinated, symptoms tend to be less severe," Biery said.

Flu symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. People with flu symptoms should stay home 24 hours after the fever is gone without the use of fever-reducing medicine.

Antiviral medications are available if given within two days of symptom onset, Biery said.

State officials said the 2009 H1N1 virus has been most common this season. That particular virus has circulated each since 2009, when it caused a pandemic.

Health officials say H1N1 typically hits younger adults and children, especially those with chronic medical conditions and pregnant women, harder than adults ages 65 and older. H1N1 was included in the 2013-14 flu vaccine, along with influenza A H3N2 and the influenza B virus.

There's still time to get a flu shot because it can take the body up to two weeks to build immunity. Officials recommend a flu vaccination for everyone 6 months and older.

Health experts say washing your hands, covering your cough or sneeze with a tissue or by using the crook of your arm, and staying home if you're sick are still the best ways to prevent the flu from spreading.

"We advise people to cover their cough and have a bottle of sanitizer near them," Beintema said. "Also, if you feel ill, don't go to work because fluid can transfer 3 to 4 feet, and in the winter people congregate closer together."